Thomson

-used a cathode ray tube and a magnetic field to determine the ratio of charge to mass (e/m) of an electron. -found electrons to be much smaller than the smallest atom (hydrogen) and that the same particles were being emitted from every type of material he used in his experiment. -concluded: 1. atoms were not indivisible 2. instead, atoms of every kind contained the same type of small negatively charged particles called electrons. 3. for atoms to be neutrally charged, their electrons must float in a positively charged substance. -developed plum-pudding model